1. Field of the Invention
The invention relates generally to the field of orthodontics and, more particularly, to computer-automated separation of a model of teeth.
2. Description of the Background Art
Tooth positioners for finishing orthodontic treatment are described by Kesling in the Am. J. Orthod. Oral. Surg. 31:297-304 (1945) and 32:285-293 (1946). The use of silicone positioners for the comprehensive orthodontic realignment of a patient""s teeth is described in Warunek et al. (1989) J. Clin. Orthod. 23:694-700. Clear plastic retainers for finishing and maintaining tooth positions are commercially available from Raintree Essix, Inc., New Orleans, La. 70125, and Tru-Tain Plastics, Rochester, Minn. 55902. The manufacture of orthodontic positioners is described in U.S. Pat. Nos. 5,186,623; 5,059,118; 5,055,039; 5,035,613; 4,856,991; 4,798,534; and 4,755,139.
Other publications describing the fabrication and use of dental positioners include Kleemann and Janssen (1996) J Clin. Orthodon. 30:673-680; Cureton (1996) J. Clin. Orthodon. 30:390-395; Chiappone (1980) J. Clin. Orthodon. 14:121-133; Shilliday (1971) Am. J Orthodontics 59:596-599; Wells (1970) Am. J. Orthodontics 58:351-366; and Cottingham (1969) Am. J. Orthodontics 55:23-31.
Kuroda et al. (1996) Am. J. Orthodontics 110:365-369 describes a method for laser scanning a plaster dental cast to produce a digital image of the cast. See also U.S. Pat. No. 5,605,459.
U.S. Pat. Nos. 5,533,895; 5,474,448; 5,454,717; 5,447,432; 5,431,562; 5,395,238; 5,368,478; and 5,139,419, assigned to Ormco Corporation, describe methods for manipulating digital images of teeth for designing orthodontic appliances.
U.S. Pat. No. 5,011,405 describes a method for digitally imaging a tooth and determining optimum bracket positioning for orthodontic treatment. Laser scanning of a molded tooth to produce a three-dimensional model is described in U.S. Pat. No. 5,338,198. U.S. Pat. No. 5,452,219 describes a method for laser scanning a tooth model and milling a tooth mold. Digital computer manipulation of tooth contours is described in U.S. Pat. Nos. 5,607,305 and 5,587,912. Computerized digital imaging of the jaw is described in U.S. Pat. Nos. 5,342,202 and 5,340,309. Other patents of interest include U.S. Pat. Nos. 5,549,476; 5,382,164; 5,273,429; 4,936,862; 3,860,803; 3,660,900; 5,645,421; 5,055,039; 4,798,534; 4,856,991; 5,035,613; 5,059,118; 5,186,623; and 4,755,139.
In one aspect, a computer-implemented method separates gingiva from a model of a tooth by defining a cutting surface along the gingiva; and applying the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
Implementations of the method may include one or more of the following. The cutting surface may be curved. The cutting surface may be expressed as a function, such as a spline function and a quadratic function. The quadratic function can be a parabolic function. The cutting surface can be interactively adjusted, wherein the interactive adjustment of the cutting surface modifies a function defining the cutting surface. The method can include interactively highlighting the separated portion and the border of the separated portion. The cutting surface can be defined by specifying a basis for the tooth. A gingival line separating a tooth surface and a gingiva can be determined. The method can include finding a high curvature location on the tooth surface. A spline can be fit to the gingival line. The cutting surface can be a plurality of surfaces. The root of the tooth can be modeled as a parabolic surface below a gingival line. The method can include defining an enclosing surface to enclose the crown of the tooth. The method also includes displaying the surface specified with a plurality of nodes; adjusting one or more nodes to modify the surface; and applying the surface to separate the gingiva from the tooth.
In another aspect, a system for separating gingiva from a tooth includes means for defining a cutting surface along the gingiva; and means for applying the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
In another aspect, a computer program, residing on a tangible storage medium, for use in separating gingiva from a computer model of a tooth, the program comprising executable instructions operable to cause a computer to: define a cutting surface along the gingiva; and apply the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
In another aspect, a computer program, residing on a tangible storage medium, for use in separating gingiva from a computer model of a tooth, the program comprising executable instructions operable to cause a computer to: define a cutting surface along the gingiva, wherein the cutting surface is expressed as a spline function and a quadratic function; and apply the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
In yet another aspect, a computer has a processor, a data storage device coupled to the processor, the data storage device containing code for use in separating gingiva from a computer model of a tooth, the program comprising executable instructions operable to cause a computer to: define a cutting surface along the gingiva, wherein the cutting surface is expressed as a spline function and a quadratic function and wherein the cutting surface further comprises a plurality of surfaces and wherein the root of the tooth is modeled as a parabolic surface below a gingival line; and apply the cutting surface to the tooth to separate the gingiva from the tooth in a single cut.
In yet another aspect, a computer-implemented method for separating tooth from gingiva includes defining a cutting surface along the gingiva; and applying the cutting surface to the tooth to separate the gingiva and reconstruct the root for the tooth in a single cut.
Advantages of the system may include one or more of the following. The system provides a flexible cutter that can be modified to follow the gingival line so user could cut off the gingiva in one single cut. The gingival line defined by user here could also be re-used later for the gingival reconstruction process.
Advantages of the invention may include one or more of the following. The system separates gingiva from tooth in a single cut. The system also reconstructs the tooth to provide a root for the tooth in the same operation. The system also generates a crown surface portion of a tooth model relatively quickly by applying the computed functions. The speed in drawing the crown surface allows real time shaping by the user when the user moves the crown control points and the top control points or when the user edits the gingival line. Also it facilitates the intersection finding itself as the system can rapidly determine whether a given point, such as a vertex of the tooth mesh, is inside or outside the gingival cutting surface.